1. Field of the Invention
The present invention relates to photography and more particularly it relates to dye developers used for photographic materials which provide images by the diffusion transfer process.
An object of the present invention is to provide dye developers, the spectral absorption characteristics of which are modified to effect a temporary hypsochromic shift in the wave lengths absorbed during exposure of an associated photosensitive emulsion and which, subsequent to exposure, can be restored to their original absorption characteristics.
Another object of the present invention is to provide novel photographic processes whereby temporarily shifted dye developers, that is, dye developers the spectral absorption bands of which have been temporarily shifted to lower wave lengths prior to exposure of a photosensitive element containing the dye developers, can be restored to their original spectral absorption characteristics subsequent to exposure of the photosensitive element.
2. Description of the Prior Art
A color image forming method employing the dye transfer process using dye developers is disclosed in the specification of U.S. Pat. Nos. 2,983,606; 3,134,764; 3,188,209; 3,255,001; 3,316,090; and 3,345,163. A dye developer is a compound having a group capable of developing an exposed silver halide emulsion and a dye portion and is a compound which is immobilized depending on the amount of the silver halide developed, with the remaining portion of the dye developer being transferred into an image-receiving element to provide a transferred image.
When such a dye developer is disposed at the exposure side of a silver halide photosensitive emulsion layer, with which the dye developer is associated, having substantially a spectral sensitivity in the spectral absorption region of the dye developer or is incorporated in the silver halide photosensitive layer, the silver halide emulsion is desensitized in appearance by the light absorption of the dye developer itself. To prevent desensitization, a method is proposed as described in the specification of U.S. Pat. Nos. 3,307,947 and 3,579,334 in which a dye developer is initially chemically converted into a compound having absorption in a shorter wave length region and then is restored to the original compound having the original absorption by reaction with a processing composition during development. However, the aforesaid patent discloses only magenta dye developers. Also, the same idea as described above is achieved for yellow dye developers in the specification of U.S. Pat. No. 3,230,085 but since the dye developers disclosed in this patent form at the same time a carboxylic acid due to the action of the alkali in the processing composition, the immobilization of the quinone moiety of the dye developer formed as the result of the development of silver is insufficient. Thus, it is difficult to avoid the occurence of the so-called "leakage", that is the occurence of certain transfer of the dye at the bright portion of the color image.
Yellow dye developers used for diffusion transfer photography are must satisfy the following criteria (1) the absorption of the dye after transfer is preferably yellow, (2) the dye has good solubility in a solvent for the dispersion of the dye in a photographic emulsion, and (3) the dye has good transfer efficiency and no transfer at the bright portion of a color image occurs. Also, a temporary short wave type dye developer must satisfy, in addition to the aforesaid criteria, the criteria that (4) the absorption of the dye developer, the absorption of which has been temporarily shifted to a short wave length side, is disposed at a sufficiently shorter wave length region, so that it does not obstruct the sensitivity of the silver halide emulsion, (5) recoloring occurs quickly due to the action of a processing composition, and (6) recoloring does not occur during the storage of the photographic material (i.e., the dye developer is stable).
The "temporary shift of the absorption region of such a dye developer to a shorter wave length side" is ordinarily attained by acylating the hydroxyl group or the amino group thereof which is an auxochrome of an azo dye. It is believed that since an azo dye can assume two tautomeric forms, i.e., a hydrazono-type tautomer having a long wave length absorption and an azo-type tautomer having a short wave length absorption, the absorption region of the azo dye can be shifted to a shorter wave length side by fixing the azo dye in the azo-type tautomer by acylation of the dye. On the other hand, few examples of such yellow azo dyes satisfing the aforesaid six criteria are known in the art; that is, in regard to, for instance, a pyrazolone azo dye, a 3-acrylazo-2,4-dihydroxyquinoline dye, a 2-arylazo-1,3-indadione, etc., the acylation thereof is utterly impossible or quite difficult; in regard to, for instance, a pyrazolobenzimidazole azo dye and a pyrimidazoloazo dye, the degree of shift of the absorption region of the dye to a shorter wave length side by the acylation of the dye is insufficient; and in regard to, for instance, an aniline-type azo dye, the acylated azo dye is not recolored by the action of a developing composition.
Furthermore, although the compounds described in the specification of U.S. patent application Ser. No. 486,730 filed July 8, 1974 may satisfy the aforesaid criteria, these compounds have insufficient solubility and transfer efficiency in using them for diffusion transfer photographic materials. Also, with respect to the hue of the image after transfer, the dye has an absorption at a slightly shorter wave length region than the absorption region of a desirable yellow dye, which requires improvement.